How large is the largest quantum coherent object possible? Unknown. The limit seems set by decoherence: thermal radiation, environmental interactions, the difficulty of maintaining phase relationships across distance. But there’s no in-principle small limit.
How about 22 micrograms, the Planck mass? Epistemic status: idle speculation. There’s this absolute mass that falls out of the fundamental constants, it must mean something.
ETA: I recently saw a report of the latest record in putting a large blob of atoms into a superposition state: 7000 sodium atoms. That’s a total mass of 23×7000 amu = 23×7000/6e23 grams = 23×7000/(6e23×22e−6) Planck masses = about 10−15 Planck masses. Only 15 orders of magnitude to go before discovering whether there’s anything in that speculation.
A Planck mass is about the mass of a medium-sized grain of sand.
How about 22 micrograms, the Planck mass? Epistemic status: idle speculation. There’s this absolute mass that falls out of the fundamental constants, it must mean something.
ETA: I recently saw a report of the latest record in putting a large blob of atoms into a superposition state: 7000 sodium atoms. That’s a total mass of 23×7000 amu = 23×7000/6e23 grams = 23×7000/(6e23×22e−6) Planck masses = about 10−15 Planck masses. Only 15 orders of magnitude to go before discovering whether there’s anything in that speculation.
A Planck mass is about the mass of a medium-sized grain of sand.
If I understand correctly, it’s smallest possible mass for a black hole.